In the most significant new downtown commercial real estate deal in years, growing cloud accounting software maker Intacct Corp. has agreed to lease about 60,000 square feet at Riverpark II, the 318,000-square-foot office tower at 300 Park Ave. that was completed in 2010 but had yet to land a major tenant.

Intacct, which sells a financial software-as-a-service product, signed the deal this week, according to two people familiar with the deal. City permit records show Intacct will be building out floors 11, 12 and 14 in the Legacy Partners-owned tower. Intacct declined to comment, but we'll update this story if that changes.

The deal, while not a blockbuster by size, is a sign of momentum in downtown San Jose and breaks an important psychological barrier. Legacy started construction on Riverpark II in 2005 and completed it in 2010 at the depths of the recession, and the building did not find a tenant. In some ways, the vacancy came to symbolize weakness in the central business district's office market.

The filling of Riverpark II's vacancy will have a significant impact on downtown's office market because the district's building base is not large. If the entire building were to fill, Class A office vacancy downtown would drop to 12.1 percent, according to Cushman & Wakefield statistics compiled and based on data current as of May 30. At that time, the brokerage showed vacancy counting the tower was hovering at about 20 percent.

For 15-year-old Intacct, the lease represents a big jump in space. It's currently in about 30,000 square feet at 150 S. Almaden. Intacct reported 153 employees to the Business Journal for its annual Best Places to Work list. (Intacct came in at No. 46 on the Midsize Employers list.)

The company's move comes on the heels of a $45 million funding round in February, bringing its total to about $135 million, according to TechCrunch.

Intacct's software tools are used by more than 7,300 companies to manage finances from the cloud. That's one area that has been slow to adopt the software-as-a-service model, according to TechCrunch, meaning there's plenty of upside for Intacct's offerings.

The company announced in a news release today that bookings for its fourth fiscal quarter increased 94 percent year over year, though the company, which is private, did not disclose specific figures.